Master of Science in Structural Engineering Design / Master of Science in Structural Engineering

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item: Thesis-Abstract
Sensitivity study of arch and cable stayed pedestrian bridges
(2023) Paulusz, NN; Baskaran, K
The configuration of pedestrian bridges varies from project to project due to project requirements. However, no single structural form can be employed for every configuration of pedestrian bridge because different structural forms have varying degrees of effectiveness. Because the functional requirements for pedestrian bridges are less constrained, designers are free to develop unique solutions that cater for potential unanticipated problems. By carefully analyzing multiple design options and engineering principles, construction professionals and civil engineers can select the optimal structural form that meets project objectives, maximizes structural efficiency, and ensures the long-term safety and durability of the built environment. Regretfully, there is still a lack of adequate instruction in these skills in engineering programs; certain small and medium-sized bridges serve as examples of this. Structural design sensitivity analysis focuses on the relationship between the design variables that the engineer can manipulate and the structural reaction that is determined by the laws of mechanics. Using this method will help you narrow down the possibilities to the ideal design solution. The research focused on several geometries and examined how different geometric requirements support structural performances in different forms, starting with alterations to a pedestrian bridge. The study's objective was to assess two possibilities and make recommendations for how they might be used to different geometric requirements. A review of the literature was done to learn more about the various types of footbridges, their functions in daily life, their significance, the evolution of bridge structures, and the components that made them up, with an emphasis on both architectural and engineering viewpoints. found footbridges with structural forms that have been studied in literature in various locations, took pictures of them, looked at geometry fundamentals, investigated the mechanism of load transmission, observed the structural details of the structures, and chose for analysis bridges with two different structural forms arch and cable stayed bridges that are believed to adhere to the social and architectural values discussed in the literature. Following an observation of the existing footbridges, a new instance was formed, design rules were developed, and two structurally similar alternatives an arch and a cable stayed bridge were presented. The modifications were made to a select few existing footbridges in compliance with the project requirements. Modified the geometry of both options by half to twice the original width, height, and span while keeping the same other measurements. After that, computer structural models were created for every scenario. By contrasting the two possibilities based on how sensitively the structural performance responds to changes in geometry, it was possible to determine the adaptability of each structural form to different geometric requirements in a project. The sensitivity analysis's findings indicate that the design changes will primarily address the arch bridge's rise to span ratio. In the short-tomedium span range, the 1:12 height-to-span ratio acts as a threshold to regulate the structure's susceptibility to geometric alterations. This indicates that if the arch bridge's rise to span ratio varies by a factor less than 1, the structure may be operating with a sizable safety margin. The analysis indicated that shallow-medium spanned arches would be efficient. In a cable-stayed bridge, the irregularity of the shape resulting from a change in geometry is evident, in contrast to arch bridges. Therefore, when constructing a cable-stayed bridge, proper proportions must be considered in addition to achieving the maximum level of structural performance. Nonetheless, it is clear that performance of the cable-stayed bridge's structure is not fully realized in the short to medium span range. Keywords: Pedestrian Bridge, Sensitivity Analysis, Bridge Form, Structural Efficiency
item: Thesis-Abstract
Construction of concrete bridges without expansion joints in Sri Lanka
(2023) Logeswaran, T; Jayasinghe, M.T.R.; Weerasinghe, P
A structure would be more sustainable if maintenance problems and associated costs are minimized. Most of the concrete bridges have been constructed in Sri Lanka with expansion joints. It results in frequent maintenance problems and associated maintenance costs, and consequently affects the durability of the asphalt pavement and impairs the ride quality as well. It is a current issue faced by RDA maintenance unit. Therefore, avoiding expansion joints will not only improve the durability of the bridge and pavement, but also results in zero maintenance cost. Expansion joints are provided to release stresses caused by movements of bridges due to the temperature variation. The temperature profile can be divided into two parts such as uniform temperature variation and non-uniform temperature variation. Uniform temperature variation causes the bridge to expand linearly while nonuniform temperature variation heats each fiber differently. Non-uniform temperature gradient can be categorized into two parts such as positive temperature gradient, which is due to rapid heating of the top fiber than the underneath fiber ; and negative temperature gradient, which is due to rapid cooling of the top fiber than the underneath fiber . When the movement caused due to the temperature changes is restrained, additional stresses would be developed in the bridge. However, the structure would be capable of withstanding those stresses if these stresses are within a reasonable range. In Sri Lanka, daily temperature variations and maximum temperature rise are not too high compared to other countries like India and Australia. Therefore, it is possible to avoid expansion joints in concrete bridges in Sri Lanka. There is no specific standard in Sri Lanka to obtain temperature values for the calculation of thermal loading except Bridge Design manual, RDA. In Sri Lanka, temperature differences for bridges can be obtained from Figure2.4 in Bridge Design manual, RDA, which is similar to Figure 9 in BS5400. These values may not be suitable to be adopted in Sri Lanka as the climatic conditions in the United Kingdom are not similar to Sri Lanka.
item: Thesis-Abstract
Behaviour of elevated temperature cured carbon fibre reinforced polymer strengthened concrete members subjected to mild acidic exposure
(2023) Koggalahewa, M.P.; Gamage, J.C.P.H.
The use of CFRP for strengthening and retrofitting concrete structures has become famous throughout the world in the past few decades due to its advantages over conventional materials. However, the main drawback to use CFRP in the construction industry is the lack of comprehensive and validated test results of its performance under different exposure environments and curing conditions. Further, the fact that using the curing temperatures near the epoxy adhesives glass transition temperature may improve the post-curing effect of the epoxy and hence improve the bond strength is still doubted during the application of CFRP as a strengthening material. A detailed experimental study was carried out to determine the effects of elevated temperature curing on the bond between CFRP and concrete and medium-term performance of such bonding methods when exposed to mild acidic environment. Three different curing conditions; ambient temperature, 650C and 750C temperature for 2 hours were selected to simulate the effects of elevated temperature curing. After fully cured for seven days, the specimens were conditioned in a sulphuric acid solution of PH=2 for 3 different time durations, 15 days, 30 days and 90 days. At the end of the exposure period, single lap shear test and Ultra Sonic Pulse Velocity test were used to assess the bond strength and the quality of the concrete, respectively. It was observed that the exposure of the epoxy to a temperature near its glass transition temperature has increased the bond strength. The bond between CFRP and concrete was sensitive to acidic exposure and a strength loss in the range of 1.74% to 26.96% was noted from conditioned specimens even though the exposure period is very short which is not a representative of a lifespan of strengthened structure or a member. The noted strength did not indicate any sensitive relationship with the curing condition and temperature in the installation phase.
item: Thesis-Abstract
Effectiveness of various outrigger systems under different structural materials for a reinforced concrete high rise building subjected to wind loads
(2022) Nissanka NAAC; Gamage JCPH
The structural efficiency of tall buildings significantly relies on the lateral stiffness of building and its resistance capacity against lateral loads. However, when the structure becomes taller and slender, the building responses under wind loads become more pivotal as it reduces structural stiffness of building. Therefore outrigger and belt truss structural systems that connect through the central core system and the most exterior columns in building are often introduced in high rise structures to provide adequate lateral stiffness in order to control the wind deflection and drift criteria in acceptable limits. Most research works are limited to building with outrigger systems of concrete material, consisting of simple square and rectangular shaped building plan layouts having vertical regularity. Only few studies were based on a single model under different patterns of outrigger structural systems to identify the optimum outrigger structural system when outrigger arrangements are varied. This study aims to bring a broader understanding of both conventional outrigger & virtual outrigger systems by identifying the most efficient lateral load resisting outrigger system for a reinforced concrete high rise building under different outrigger structural materials of concrete, steel and composite by comparing the performance for three different outrigger arrangements; only outriggers, only belt truss and combination of both outrigger and belt truss when subjected to wind loads while their positions remain constant for all the three cases. The structural performance was evaluated based on building frequency, wind induced lateral displacement at top storey and inter storey drift ratio and results demonstrate that addition of outriggers and belt trusses of different structural materials have significantly enhanced the structural performance of building against wind action and the best form of outrigger structural arrangement is varied based on each structure material.
item: Thesis-Abstract
Experimental analysis of curved RC beams strengthened with carbon fibre for flexural and shear capacity enhancement
(2022) Premalal RPDS; Gamage JCPH
Among the concrete strengthening applications, Carbon Fibre Reinforced Polymer (CFRP) systems offer better mechanical properties than other alternatives, such as stronger tensile strength, stiffness, and durability. Most of the studies have been focused on strengthening or retrofitting straight Reinforced Concrete (RC) beams using CFRP, fewer on the horizontally curved out of plane loaded RC beams, which are present in novel featured structures worldwide. In contrast to straight beams, the curved beam behaviour possess combined effect of bending, torsion and shear where CFRP application requires a careful selection based on the intended capacity enhancement. The experimental program includes total 6 nos. of RC beam specimens of fixed curvature casted, 2 beams weak under shear and 2 beams weak under flexure and their control beams. The CFRP strengthening was applied as relevant to evaluate the effectiveness of flexural and shear enhancement. The NSM CFRP plate application and end anchored NSM CFRP for flexure strengthening along with 450/1350 oriented CFRP fabrics at beam sides and increased area of fabric for shear strengthening was focused. The specimens were tested using four point bending test and the ultimate failure load, crack patterns, failure modes and deflection was observed. The experimental results under flexure concluded that NSM CFRP enhance flexural strength according to the initial cracking load observations. Where end anchored CFRP fabric provided it contribute to additional flexure strength and reduce overall deflection by 23%. Ultimate load carrying capacity of NSM CFRP retrofitted beams were enhanced by 12.1% and 8.4% for respective application. NSM CFRP retrofitted beams showed, lesser crack density and widths. Propagation of the crack which was in the direction of NSM CFRP plate corners is restrained with the use of end anchored CFRP, although its effect over shear capacity enhancement is insignificant. The experimental flexural enhancements are 28.8% and 29.3% less than the theoretically predicted values by ACI 440.2R-17 guide, respectively for NSM CFRP only and end anchored beams, which may have occurred due to the contribution of additionally induced torsional stresses. iv The experimental results under shear concluded that ultimate load carrying capacity of shear retrofitted beams were enhanced by 20 % and 30%. The influence of CFRP retrofitting is higher when the CFRP application area is increased at inner shear span. The experimental shear enhancements are 35.4% and 20.3% less than the theoretically predicted values by ACI 440.2R-17 guide, respectively for side laminated and extra side laminated beams. The intermediate debonding and induced additional torsional stresses may have caused this capacity reduction.
item: Thesis-Abstract
Retrofitting of reinforced concrete curved beams failed in shear under out of plane loading using carbon fibre reinforced polymer
(2022) Senaratne SAMANI; Gamage JCPH
Carbon Fibre Reinforced Polymer (CFRP) strengthening techniques have gained popularity compared to other retrofitting methods due to its superior performance. While ample research had been done regarding retrofitting of straight beams that have failed in shear, as per the author’s knowledge no research has been done regarding the retrofitting of curved beams that have failed in shear under out of plane loading. Due to the curvature of the beam, bending, shear and torsion all act together in resisting loads and hence it is important to study the effects of these on CFRP retrofitted curved beams. An experimental study consisting of four curved beams of 2m and 4m radii of curvature, which had previously failed under the combined effect of shear and torsion for out of plane loading were selected and were externally retrofitted using CFRP strips. The beams were then re-tested for their new failure loads and the load carrying capacities were compared with their original values. From the experimental program it was observed that two beams exhibited load carrying capacities of 122% and 117% of their original value while the other two exhibited load carrying capacities of 85% and 90%. The predominant mode of failure was CFRP strip de-bonding from its substrate. Therefore it was identified that by anchoring the CFRP strips to the substrate the carrying capacity could be significantly increased by delaying de-bonding load by distributing stresses across two of more CFRP strips.
item: Thesis-Abstract
Steel portal frame design for deconstruction and reuse
(2022) Surendra KI; Hettiarchchi MT P
Today, the world over, much emphasis is focused on the use of sustainable materials in infrastructure. One of the main attributes that has led to the widespread use of steel in infrastructure is that is considered sustainable. Steel meets the 3R concept of Sustainability, Reduce, Reuse and Recycle. While steel components are 100% recyclable, the manufacture of stronger and better quality steel products has enabled the design and construction of structures using reduced quantities of steel. Due to scarcity of raw material, conservation of energy coupled with escalation of steel prices, it is prudent to design steel structures that can be re-used, thus extending the life cycle of steel. This is an aspect that has hitherto not received sufficient consideration by structural engineers. The focus of this thesis is on extending the life cycle of steel components, with particular emphasis on the design of single span steel portal framed structures by considering the aspects of deconstruction and re-use. The scope of the study was limited to a span range of 20m to 40m and eaves heights of 4m and 6m and typical vertical action of 10kN/m. The adoption of haunches hinders the re-use of the rafter. An innovation recently adopted facilitating the re-use of rafters is that of replacing the haunch at the eaves with a steel knee brace pinned at either end to the column and rafter. This concept was investigated and found to be viable within this range of span and eaves heights. Optimum locations for knee brace connections were found to be 10% of span length at the rafter end and 3% of the span length from the rafter axis at the column end. These initial studies indicate that greater attention should be paid on the aspect of deconstruction and re-use of steel at the preliminary stages of design in order to extend the life cycle of steel components and thereby enhance the sustainability of steel structures.
item: Thesis-Abstract
Cost Implications of adopting eurocodes for steel concrete composite bridges in Sri Lanka
(2022) Abeysuriya AN; Jayasinghe MTR
Construction of concrete bridges gained popularity after the introduction of pre-stressed concrete in 1950s, due to low cost of maintenance and locally available construction material. The concrete bridge industry was developed, so that reinforced and pre-stressed concrete bridges were designed and constructed in Sri Lanka. Steel being imported material that require maintenance, steel bridge industry was not developed. Although with present high-grade steel, durable protective systems, steel composite bridges offer competitive designs for longer spans, locations with poor ground conditions, accessibility problems due to congested traffic and remote locations. BS5400-2 (1978) and R.D.A Bridge design Manual remained as the main bridge design standards during past few decades up-to-date. Pre-tensioned beams used in the road network are still produced, and bridges are designed for these standards. BS design standard need to be replaced with Eurocode standard since BS standards will not be updated in future. This study selected UK National Annex for traffic loads (NA to BSEN 1991-2:2003) to compare with current BS 5400-2 loading adopted in Sri Lanka. Standard simply supported bridge decks with two traffic lanes (carriageway 7.4m) and two footways on either side considered in this study. Standard pre-tensioned concrete beam deck spans 9.04m – 24.54m and composite designs made for this study for spans 31.5m – 50m considered in the comparison of traffic loads of BS5400-2 (1978 & 2006) and Eurocode UK National Annex. Culverts and existing bridge span up to 9.0m were not considered to maintain the simplicity of this study. iii In order to compare deck costs, existing concrete decks were estimated based on Highway Schedule of Rates (HSR) and past construction data. Designs and estimates were prepared for recommended UKNA loading for steel composite bridges for spans 11.5m – 50m. The cost information provided from a steel fabricator and published data together with past construction data were considered in the estimation of composite decks. This study recommends suitable UKNA loading, to replace current BS loading and identifies economical span range for steel composite bridges designed, when compared with existing concrete bridge types for prices prevailed in 2020. Identical costing process could be repeated with latest prices and HSR rates to for comparison of cost between concrete and steel concrete composite decks in future years.
item: Thesis-Abstract
Behaviour of carbon fibre reinforced polymer retrofitted, out of plane curved reinforced concrete beam failed in flexure
(2022) Indrachapa TH; Gamage JCPH
Due to their superior qualities in contrast with the alternatives, Carbon Fibre Reinforced Polymer (CFRP) strengthening techniques have proven great performance in externally strengthening Reinforced Concrete (RC) elements. The behavior of externally CFRP strengthened RC elements has been the subject of numerous studies. However, to the authors' view, whereas the majority of studies have concentrated on externally reinforcing straight RC beams with CFRP, none have focused on strengthening horizontally curved RC beams. The use of curved beams was significantly increased due to development of infrastructure and high concerns on aesthetical appearance. Hence, curved beams naturally respond to shear, torsion and flexural effect. In a similar way, the industry need to be more focused on the way to respond in flexural failure in such a case. As a result, it's crucial to investigate the possibility of the retrofit when a beam failed in flexural effect. The experimental approach was carried out in order to reduce the aforesaid research need. A series of 2m and 4m radii beam specimens were tested in 2 stages with CFRP shear strengthen and retrofit the beams which are failed due to flexural effect.
item: Thesis-Full-text
Eurocode loads and its implications to design of box culverts in Sri Lanka
(2022) Sumanasinghe AKYB; Jayasinghe MTR
The Box Culverts are drainage structures that allow to cross, small to medium scale water paths. They generally founded in soil where scouring is not an issue. The advantage of the box culvert is that it can be rested on the soil where low bearing pressures exists. Box culverts are also often used in expressway construction when underpasses are needed for the traffic of by-roads that crosses the expressway embankment. The present highway structure design practice in Sri Lanka is based on the British Standards of BS 5400 that was published by British Standard Institution (BSI) in 1978 and then amended a number of times subsequently and along with the Bridge Design Manual (1991), Published by Road Development Authority, the apex body of managing A & B class of road in Sri Lanka. Since the BS codes have been superseded by BS EN (the English version of Euro Codes) in March, 2010, it is now opportune to adopt the recommendations of BS EN for the structural design of highway structures and hence box culvert design will also need updating. In the research presented, a detailed study has been carried out as a comparative study by considering number of possible arrangements of Box Culverts that are typically used in Sri Lanka. The reason is that BS EN allows a loading regime from which different values can be selected in contrast to the current BS based practice. The detailed analysis, with finite element method (FEM) , have been carried out for different types of loading specified in the BS EN; the results have been compared with the resulting forces due to the currently adopted standards to find suitable loading levels that can be recommended for the adoption of Sri Lanka. The results are presented in graphical form to allow the selection of different levels of loading based on the effects on the main design parameters.
item: Thesis-Abstract
Development of earthquake resistant design guidelines for bridges in Sri Lanka
(2022) Kumara MAC; Lewangamage CS; Baskaran K
Sri Lanka is an island located on the Indo-Australian tectonic plate and the location of the country is far away from the plate boundary where inter-plate earthquakes are possible to occur. However, there are earthquake records during the recent past which have considerable magnitude. Moreover, intraplate earthquake risk is there which is possible to occur without prior warning. Therefore, Sri Lanka is no longer be considered safe from seismic threats. With the increasing demand to improve the road network in the country, it is necessary to reconstruct existing bridge structures. However, there are no seismic design guidelines to use for bridge design procedure in Sri Lanka. This study is therefore aims to formulate earthquake-resistant design guidelines for bridges in Sri Lanka. For the purpose of formulating the design guideline, bridge classification into three different important classes is proposed based on the relevant classifications in similar codes such as EN 1998-2:2005 , IS 1893-3:2014 and AS 5100.2-2004. Important factors and return periods are proposed based on the guideline given in EN 1998-1:2004. Further, Elastic response spectrums for rock or hard soil are selected based on the available response spectrum for Sri Lanka. However, there is no response spectrum defined for medium soil and soft soil. Therefore, it is proposed to use the response spectrum available in IS 1893-1:2002 for medium and soft soil since soil and rock types are more similar when both countries lie on the same tectonic plate. This study proposed a seismic analysis approach for bridges using either EN 1998-2:2005 or AS 5100.2-2004. Moreover, suitable design parameters such as peak ground acceleration values are proposed to select according to the available national data. iv There are three case studies carried out to illustrate the use of developed guidelines for seismic analysis of bridges in Sri Lanka. Three Case studies were carried out for bridges in the category of important class I, important class II and important class III by using the design codes of AS 5100.2-2004, IS 1893-3:2014, and EN 1998-2:2005. For case study 1, base shear values were calculated using the static lateral force method of analysis and three different design codes provided different results of 50kN, 51kN, and 36kN. For case studies 2 and 3, static analysis was carried out using selected three design codes, and response spectrum analysis was carried out according to EN 1998-2:2005 using the response spectrum defined for rock or hard soil of Sri Lanka. Base shear values of the static analysis results provide different values for three design codes. However, a comparison of the results of response spectrum analysis and fundamental mode method of analysis for Eurocode 8-part2 as the basis of analysis, provided similar fundamental period values and base shear values for both methods. Results of the case studies illustrate that when the design basis is Eurocode 8-Part 2, it provides an average or lower result of base shear value. Since Eurocode 8 provides an opportunity to use it with national choices, it is more suitable to use EN 1998-2:2005 with a national annex for bridge design. Therefore, a developed guideline with national parameters can be used for the seismic design of bridges in Sri Lanka.
item: Thesis-Abstract
Investigation on applicability of ultrasonic pulse velocity measurements to estimate thickness of reinforced concrete wall panel
(2021) Fazli ZTM; Nanayakkara D
In Sri Lanka, Concrete has been widely used as a construction material for more than hundred years and it is necessary to analyse some of these existing old structures to check their structural adequacy, for retrofitting works, repair works and rehabilitation works, etc. For these purposes it is necessary to know the sectional dimensions of structural elements and reinforcement details to evaluate the structural adequacy with the existing strength of concrete. In most of the cases it may not be possible to find the structural drawings to obtain these required structural details and also it may not be possible to measure the required thicknesses of structural elements due to accessibility problems. The objective of this research study is to establish a suitable non destructive method to estimate the thicknesses of various types of concrete members with accessibility problems. Hence, from a thorough literature study, it was found that using ultrasonic pulse velocity methods it could be possible to determine the uniform thicknesses of concrete walls. It is reported that this ultrasonic pulse velocity is affected by the concrete properties as well as the other factors such as temperature, stress history/ level of stress, path length, moisture and curing condition of concrete, presence of reinforcement and size and shape of the specimen. Accordingly, testing was conducted to study the influence of reinforcement percentages and to observe the influence of some other parameters such as age of concrete, moisture condition and temperature on the accuracy of the thickness predictions using ultrasonic pulse velocity method. Further to verify the results, some existing structures were also investigated. From this experimental study and the field investigations, it is found that the UPV test method could be used to estimate the thickness of concrete walls with a reasonable accuracy.
item: Thesis-Abstract
Retrofitting of punching shear damaged flat slabs using carbon fiber reinforced polymer (CFRP) sheets
(2021) Priyanjani VGM; Gamage JCPH
The punching shear failure of flat slabs is common in reinforced concrete buildings, and once the failure occurs, rectification is difficult and time consuming, which also affects building functionality. Hence, it is convenient to retrofit the flat slab structure to enhance the punching shear capacity while minimizing the disturbance to the structure. Therefore, a method was developed to retrofit punching shear damaged flat slabs using Carbon Fiber Reinforced Polymer (CFRP) sheets, considering the advantageous properties of the material, like the flexibility of usage, less weight, less thickness of material etc. Thus, experimental and theoretical studies were carried out using 12 numbers punching shear failed flat slab panels with various repair materials and various CFRP sheet arrangements. The BS EN 1992-1-1: 2004 standard was used for theoretical analysis. A comparison of theoretical and experimental punching shear capacities concluded that the theoretical capacity is much higher than the experimental capacity, due to the difference of failure modes of the specimens.
item: Thesis-Abstract
Study and analyse the excessive camber development in precast prestressed slab panels
(2021) Gamage MDD; Baskaran K
In Prestressed concrete, the initial compression is applied to the concrete before applying any external load so that stress from external loads is counteracted in a favourable way. Camber in precast prestressed slab panels can be defined as the upward deflection that is caused due to the moment caused by the eccentric prestressing force. Excessive camber development in precast prestressed slab panels can lead to several problems such as needing extra amount of topping concrete meaning extra cost and extra dead load. In addition, cracking of top surface of slab leads to durability problems. Therefore, accurate prediction of camber is essential to minimize these problems. The objective of this research is to identify the causes for the difference between design and actual camber and to propose suggestions to minimize excessive camber in precast prestressed slab panels. To achieve the research objective, a literature review was carried out to identify camber calculation methods in precast prestressed slabs and to identify the reasons for difference between calculated and actual camber. Then did manual calculations for designing of sample precast prestressed slab panel. Electronic strain gauges were installed to high strength strands to measure the strain developed in the strands during stressing and destressing processes and obtained the data logger readings. Then comparative analysis of literature review findings, theoretical calculations and practical observations were done, and the conclusion was derived based on above analysis results. From the recalculation process by using the material properties and parameters obtained by experimental data, it is shown that it is adequate to use 5 number of strands instead of 6 number of strands. From the experimental values obtained from concrete cylinder tests, the actual Modulus of Elasticity in concrete used is lower than the values considered in design. When the Modulus of Elasticity of concrete decreases, the upward deflection also increases. Because of excessive camber development we had to put extra amount of topping concrete thickness to maintain the minimum topping concrete layer thickness of 75 mm and to maintain levelled floor surface. This increases extra 5.27% of topping concrete material cost. Stress releasing process of strands was done one by one and is not symmetrical. Therefore, the stress at strands varies during the releasing process. Due to this reason, there can be a twist in the precast prestressed slab panel and the camber value also varies along a cross section considered. Therefore, it is suggested to release all strands simultaneously.
item: Thesis-Abstract
Investigation of effects of bonding agent on performance of cold joint in concrete member
(2021) Pushparuban P; Gamage JCPH
One of the most common difficulties in the execution of concrete structures is cold joint because of delay in concrete casting due to several circumstances as well as improper casting sequence. The discontinuity in concrete element leads to structural weakness, increasing the permeability, corrosion of the reinforcement, reducing the durability and bad appearance of concrete. In this research, the aim to eliminate the cold joint by applying the bonding agent. In order to evaluate the effect of the bonding agent on cold joint, 76 number of cubes were cast using grade 30 concrete. Out of them, 36 specimens contain cold joint with 20° degree of inclination to the horizontal plane for compressive strength with and without applying bonding agent other 36 specimens had cold joint in the horizontal plane for splitting tensile strength with and without applying bonding agent and considered delay time of one hour interval up to 5 hours. After 28 days of curing, all specimens were tested as per standard method. The experimental result of compressive strength shows that cold joint with applying bonding agent give 6% improvement as compare to without applying bonding agent. But, the experimental result of splitting tensile strength shows that no considerable influence on cold joint as applying bonding agent compare to without applying bonding agent. However, there is considerable reduction in the compressive strength (30.50%) and tensile strength (33.14%) compare with initial specimens with applying bonding agent. Further, observation based on failure surface of tested specimens clearly indicated that, there are no aggregate inter logged in between two layers when delay time past the initial setting time of the first layer. So, the reduction in strength due to the cold joint purely depends on aggregate interlocking. The better options are to avoid the cold joint by using admixtures (retarders) to increase the initial setting time, adopt proper casting sequences and vibrate the layers together even within the initial setting time.
item: Thesis-Abstract
Comparative study of design inputs in design of overhead transmission line towers
(2021) Aluthwaththa AGHAD; Baskaran K
The Ceylon electricity board is the main electricity producer in Sri Lanka. The supply arm of the Ceylon electricity board is divided into three categories: Generation, Transmission and Distribution. The power lines having the capacity 132 kV and above comes under the transmission category. The transmission lines may be spanning over a few kilometres to hundreds of kilometres, depending on the power station location. The lattice towers are the main supporting structures in the transmission line. The cost of the transmission towers is ranging from 28 to 40 percent of the total cost of a transmission line project. Every year the power demand may increase by around 10 %. To have uninterrupted power supply the Ceylon Electricity Board must increase its supply capability simultaneously. With this huge power demand CEB must move to 400 kV lines in the near future. The scarcity of new corridors to build new lines demands increase the capacity of the existing lines by using the same corridors. Both requirements demand heavy towers. The design of the transmission towers and foundations is done according to the CEB specifications, which were produced long ago. The CEB specification is based on the probabilistic method with safety factors while the world is moving towards the reliability-based method. The CEB towers are known to be the heaviest towers in the region. The largest existing tower uses the maximum available angle iron as the leg members. When increase the tower capacity and the number of circuits to four circuits from two, star angles or combined angles must be used as the leg members. The foundations have to be designed either as raft foundations instead of single footings or pile foundations in fairly good soils. The towers need to be optimized in order to overcome the limitations in the design as well as to reduce the cost of the projects. The lattice towers are designed for decades and the optimum tower configuration have been already identified by the designers. The optimization of the design input is the next possible approach to design an optimized tower. The design inputs mainly depend on the code of practice used in the design. In this research, an attempt was made to identify the economic viability of the CEB design inputs against IS 802:1:1 (2015) and IEC 60826 (2017) design inputs. The objective of the research was achieved by identifying the different design inputs against different codes of practices and design two type towers, one line tower (TDL) and one angle tower (TD3) in PLS tower software by using the identified design inputs. The design was carried out according to the ASCE 10:97 and IS 802:1:2 (2016). To identify the economic viability of the design inputs the support reactions and the member capacity usages were compared using the output of the FEM. As per the results that the tower weight and the foundation size could be reduced by a significant margin if the design was carried out by using either IS or IEC codes instead of the CEB specifications.
item: Thesis-Abstract
Effects of elevated temperature curing on glass transition temperature of CFRP/ concrete bond
(2021) Rathnasiri WKK; Gamage JCPH
Strengthening of existing structures made out of concrete, all around the world is an increasing requirement due to many reasons like aging, insufficient maintenance, and the degradation due to environmental impact, as well as due to increases of the applied loads and due to requirement of complying with the modern standards. Carbon Fiber Reinforcement Polymer, CFRP, one of the budding and potential technologies in the structural strengthening process. As such lots of researchers who wish to continue their higher studies and knowledge gaining in structural engineering have involved researchers in structural strengthening using CFRP. Laying CFRP fabrics and composites using epoxy adhesives, along the external surfaces of structural elements are the popular method for a strengthening of structural capacities. These externally laid CFRP fabrics are subjected to elevated temperatures due to environmental conditions. The exposure to such elevated temperature affects the strength of the CFRP/Concrete bonds, because of the low glass transition temperature (Tg) of these epoxy adhesives that have been used to create the bond between CFRP and concrete substrate. A slight increment of Tg is also contributed to enhancing environmental resistance of strengthened outdoor members which directly expose to the environmental fluctuations. Curing of the CFRP/epoxy/concrete bond in an elevated temperature environment may enhance the bond performance while improving its Tg. However, it is important to ensure a safe temperature range in curing without affecting the performance of the concrete part of the system. This study focuses on determining the safe temperature range, which may be used as raised temperature curing of the CFRP/Concrete composites and determination of bond characteristics for the corresponding temperature applied for curing. A total of twenty-five single strap joints were prepared under two different curing conditions. The impact of curing at moderately elevated temperature (75°C) on CFRP/Concrete bond strength was examined for both ambient and elevated temperature conditions.
item: Thesis-Abstract
Simulation of wind response of tall buildings using computational fluid dynamics - a case study
(2021) Siriwardana KDYE; Mallikarachchi HMYC
few decades. Interaction of wind with buildings with complex geometry leads to a complex building-wind environment. However, all codes of practice and standards are only applicable for buildings with simple geometry and height limitations. Moreover, all wind codes mainly present static based calculation. Generally, the static analysis is suitable only for structures less than 50 m height. Therefore, the actual wind effect is difficult to assess by the wind loading codes, hence recommend using Computational Fluid Dynamics (CFD) models. In this research, wind loads and its effects are calculated on a 31-storey high rise building utilizing three different international wind loading codes/standards, namely CP3 CHAPTER V-2:1972, BSEN 1991-4:2005 with SLS EN 1991-1-4:2019, AS/NZ 1170.2:2011 by encountering different factors and methods specified. The estimated forces are compared with each other since the different codes introduced different factors to estimate wind turbulent characteristics. Numerical Simulation has been carried out for the same building using RANS approach (Spalart-Allmaras). Comparison is carried out between the results obtained from simulation and code based calculations. This study has been used to evaluate the applicability / limitations of codes of practice via numerical simulation and identify the more suitable wind loading code. AS/NZS 1170.2:2011 is more suitable to evaluate the wind loads and their effects on tall buildings due to its advanced flow parameters. In addition, S-A turbulent model well performed in evaluating the complex building – wind environment accurately and different flow features such as vortices, wake formations etc. are clearly observed. The advantages of commercially available CFD software on complex fluid -structure problems has been discussed in terms of time, cost and accuracy of results opposed to other methods such as codes of practice and wind tunnel testing.
item: Thesis-Abstract
Comparison of eurocode 2 and BS 8110 recommendations for the design of bending and deflection in simply supported one way slabs
(2021) Ahamed AAH; Dias WPS
Recently in Sri Lanka, design of the civil structures is adopted by Eurocodes superseded by the British code of practices. For reinforced concrete structures the Eurocode 2 will became of paramount importance to the design of the structural members. Bending and deflections are most important governing criteria in designs of slabs. Both standards for reinforced concrete design to check the deflection control by mean of minimum member thickness requirement and a direct computation method. This research covers an analytical study that compared maximum span to depth ratios on deflection on different influence factors in simplified method and rigorous method. One-way slab on simply supported slab was considered to compare the parameter to compare in the research. Further the deflections were compared with an experimental result produce by Gilbert (2004) with numerical calculation with respect to both code recommendation and its reliability was discussed. The influence factors on deflection and bending were analyzed in term of sensitivity factors to understand the variation on results. The results indicated the EC2 predict less area requirement for the flexure and a very thin slab can be used to control deflection if the applied moment not induced any crack in the element and the increased in tensile strength and Elasticity of concrete provide more sophisticated deflection control compared to the BS 8110.
item: Thesis-Full-text
Implications of Eurocode for steel portal frames in Sri Lanka
(2019) Premachandra KISG; Hettiarachchi MTP
Portal frame structures are widely used all over the world and in Sri Lanka for warehouses and factory buildings as they allow a large column free area with a maximum open space. They are basically made out of steel. Speedy construction, flexibility in use and easy maintenance are the main advantages in steel portal frames. Up until now in Sri Lanka, steel portal frames were designed mainly according to the British standards. But Eurocode is a more updated set of guidelines formed through research and experience. This paper investigates the implications of Eurocode for steel portal frames in Sri Lanka. A field survey was carried out via questionnaires and responses in interviews to get a firsthand understanding of portal frame structures prevalent in Sri Lanka. With this experience, 48 different portal frames were selected for the parametric study to suit the Sri Lankan conditions varying the span range from 20m to 50m, eaves height from 4.5m to 6.0m and frame spacing from 4.5m to 9.0m. They were analysed to find the implications of Eurocode based on the methods proposed by the Steel Construction Institute. Results of parametric study were compared with each other and with available literature and publications. Identified implications are discussed in this paper concerning forces, moments and weight variations. A table was developed to obtain optimum column and rafter sections for selected ranges of parameters. No significant advantages were found in designing portal frames to elastic theory based on Eurocode compared to British standards in terms of weight. Main frame weight as a percentage of ULS axial force of a column (excluding the self weight of frame) was found to be in the range of 10% to 45% for 4.5m eaves height frames and 18% to 45% for 6.0m eaves height frames